diff --git a/.htmltest.yml b/.htmltest.yml
index 109d0012b..f9cbd73f4 100644
--- a/.htmltest.yml
+++ b/.htmltest.yml
@@ -31,6 +31,7 @@ IgnoreURLs:
 - "https://dotnet.microsoft.com/.*"
 - "https://scribehow.com/.*"
 - "https://www.rabbitmq.com/.*"
+- "https://letsencrypt.org/.*"
 IgnoreDirs:
 - "docs/?.*/_print/"
 - "docs/?.*/_shared/"